DEVELOPMENT OF THE FROG S EGG. 279 



show that the results with these eggs are not due so largely to 

 osmotic pressure, but more to some chemical action which ap- 

 pears to take place between the constituents of the egg substance 

 and sugars or salts when contained in fresh-water solutions. It 

 may be that something present in the usual medium in which 

 they develop, the sea water, prevents to some extent such an 

 action, thus both salts and sugar act less violently when applied 

 in sea-water solutions. The physiological condition of the egg 

 may be weakened in fresh water as is indicated by its slightly re- 

 tarded development in this medium, and under such circumstances 

 they may be more susceptible to external injurious influences. 

 It is possible that new substances may be formed when sugar 

 is added to salt solutions since some salts, e. g. t NaCl may form 

 sodium-sugar compounds. Such compounds might be more or 

 even less toxic than the original chemicals from which they re- 

 sulted. These suggestions, which are at best speculative, serve to 

 show how far we are from an understanding of the manner in 

 which eggs respond to chemical stimuli, and indicate the impor- 

 tance of obtaining more complete data on the subject. 

 Zoological Laboratory, 



Columbia University, May, 1907. 



